Contract Balances and Performance Obligations - Contract Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Contract with Customer, Liability, Current	$ 115,100	$ 111,000
Contract with Customer, Liability	122,141	116,320	$ 108,118
Contract with Customer, Liability, Revenue Recognized	(101,640)	(93,265)
Contract With Customer, Liability, Excluding Revenue Recognized	107,461	101,467
Contract with Customer, Liability, Noncurrent	$ 7,000	$ 5,300